This project focuses on a novel vasopressin-activated calcium-mobilizing (VACM-1) receptor. We have cloned a cDNA encoding VACM-1 receptor which contains 780 amino acids. VACM-1 has binding properties expected of a vasopressin receptor and is functionally coupled to the mobilization of cytosolic free calcium (Ca2+). The deduced amino acid sequence of VACM-1 does not have significant homology with any nucleic acid sequence yet reported, including the V1 and V2 AVP receptors. Thus, it is possible that VACM-1 represents a novel receptor family. We hypothesize that VACM-1 receptor may bind a ligand that is more specific than vasopressin. Partial acid hydrolysis of this fraction and analysis by thin layer chromatography (TLC) revealed presence of amino acids not identical to those found in hydrolyzed AVP, thus suggesting that the new ligand may be a peptide. Consequently, the specific objective of this proposal is to identify this putative ligand. Specifically, we have isolated this putative new ligand and are characterizing it by MALDI-MS and PSD analysis. Once we have identified the ligand, it will be synthesized and tested in cells expressing VACM-1 in vitro.